#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    int ret, cnt, m, n;
    bool vis[20][20];
    int dx[4] = { 0, 0, 1, -1 };
    int dy[4] = { 1, -1, 0, 0 };
    int uniquePathsIII(vector<vector<int>>& grid) {
        int x = 0, y = 0;
        m = grid.size();
        n = grid[0].size();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == 1)
                    x = i, y = j;
                else if (grid[i][j] == 0)
                    cnt++;
            }
        }
        cnt += 2;
        vis[x][y] = true;
        dfs(grid, x, y, 1);
        return ret;
    }
    void dfs(vector<vector<int>>& grid, int i, int j, int step) {

        if (grid[i][j] == 2) {
            if (step == cnt)
                ret++;
            return;
        }
        for (int k = 0; k < 4; k++) {
            int x = i + dx[k], y = j + dy[k];
            if (x >= 0 && x < m && y >= 0 && y < n && !vis[x][y] &&
                grid[x][y] != -1) {
                vis[x][y] = true;
                dfs(grid, x, y, step + 1);
                vis[x][y] = false;
            }
        }
    }
};